Aqueous dispersions of cross-linked polymer microparticles

Abstract

The invention relates to aqueous dispersions of cross-linked polymer microparticles, prepared in an aqueous medium from a polymer, optionally dissolved in an organic solvent, said polymer bearing at least two hydroxyl groups and comprising a number of ionic groups sufficient for the formation of a stable aqueous dispersion, as the component (A) and one further component (B) at an elevated temperature, characterized in that component (A) is a polyesterpolyol, a polyurethane or a polyacrylate having an acid value of from 5 to 168, and that component (B) is an aminoplast resin consisting of molecules containing at least two reactive groups consisting of hydroxyl and/or amino and/or ether groups, that the ratio by weight of component (A) to component (B) is between 30:70 and 95:5, and that the dispersion is stable and usable in water and/or an organic solvent or mixtures thereof. The invention further relates to a process for producing these dispersions, the use thereof and coating compositions containing said dispersions.

It is claimed: 
     
       1. An aqueous coating dispersion of cross-linked polymer microparticles, said polymer microparticles being prepared at an elevated temperature in an aqueous medium from two components, (A) and (B), the ratio by weight of component (A) to component (B) being between 30:70 and 95:5, wherein A. component (A) is a polymer, optionally dissolved in an organic solvent, said polymer bearing at least two hydroxyl groups and comprising a number of ionic groups sufficient for the formation of a stable aqueous dispersion, said polymer comprising a polyesterpolyol having an acid value between 20 and 50, said polyesterpolyol being prepared from one or more polyol(s) selected from the group consisting of: ethylene glycol, 1,2- and 1,3-propanediol, 1,3- and 1,4-butanediol, the isomeric pentanediols, hexanediols or octanediols (e.g., 2-ethyl-1,3-hexanediol), trimethylolpropane, neopentyl glycol, glycerol, bishydroxymethyl cyclohexane, erythritol, mesoerythritol, arabitol, adonitol, xylitol, mannitol, sorbitol, dulcitol, hexanetriol, and (poly-)pentaerythritol, by reaction with one or more polycarboxylic acid or anhydrides thereof--so far as said anhydrides exist--having from 2-18 carbon atoms, wherein said polycarboxylic acids and/or anhydrides may be employed individually or in admixtures thereof; and   component (B) is an aminoplast resin consisting of molecules containing at least two reactive groups consisting of hydroxyl and/or amino an/or ether groups;   the aqueous dispersion of cross-linked microparticles being stable.   
     
     
       2. The dispersion according to claim 1, characterized in that methylolated melamine resins are employed as the component (B). 
     
     
       3. The dispersion according to claims 1 or 2, characterized in that the ratio by weight of component (A) to component (B) is between 60:40 and 80:20. 
     
     
       4. The dispersion according to claims 1 or 2, characterized in that the component (B) is added into the solution of the component (A) in an organic solvent or solvent mixture, the mixture is neutralized to a degree of from 70% to 90%, and preferably of 80%, with an aqueous solution of an amine, and the resulting mixture is heated to a temperature of from 50° C. to 100° C., and preferably from 70° C. to 90° C., to reach a constant viscosity, and then is neutralized up to 100% with the amine. 
     
     
       5. The dispersion according to claims 1 or 2, characterized in that the organic solvent or solvent mixture is distilled off after the complete neutralization. 
     
     
       6. A process for producing an aqueous coating dispersion of cross-linked polymer microparticles, said process comprising reacting two components, component (A) and component (B) by: (a) adding component (B) into a solution of component (A) in an organic solvent or solvent mixture, the ratio by weight of component (A) to component (B) being between 30:70 and 95:5;   (b) at least partially, neutralizing the mixture;   (c) heating the mixture in an aqueous medium wherein 1. component (a) is a polymer optionally dissolved in an organic solvent, said polymer bearing at least two hydroxyl groups and comprising a number of ionic groups sufficient for the formation of a stable aqueous dispersion, said polymer comprising a polyesterpolyol having an acid value between 20 and 50, said polyesterpolyol being prepared from one or more polyol(s) selected from the group consisting of: ethylene glycol, 1,2- and 1,3-propanediol, 1,3- and 1,4-butanediol, the isomeric pentanediols, hexanediols or octanediols (e.g., 2-ethyl-1, 3-hexanediol), trimethylolpropane, neopentyl glycol, glycerol, bishydroxymethyl cyclohexane, erythritol, mesoerythritol, arabitol, adonitol, xylitol, mannitol, sorbitol, dulcitol, hexanetriol, and (poly-)pentaerythritol, by reaction with polycarboxylic acid or anhydrides thereof--so far as said anhydrides exist--having from 2-18 carbon atoms, wherein said polycarboxylic acids and/or anhydrides may be employed individually or in admixtures thereof; and   2. component (B) is an aminoplast resin consisting of molecules containing at least two reactive groups consisting of hydroxyl and/or amino and/or ether groups;     (d) obtaining a stable aqueous dispersion of cross-linked microparticles.   
     
     
       7. The process according to claim 6, characterized in that methylolated melamine resins are employed as the component (B). 
     
     
       8. The process according to claims 6 or 7, characterized in that the ratio by weight of component (A) to component (B) is between 60:40 and 80:20. 
     
     
       9. The process according to claims 6 or 7, characterized in that the component (B) is added into the solution of the component (A) in an organic solvent or solvent mixture, the mixture is neutralized to a degree of from 70% to 90%, and preferably of 80%, with an aqueous solution of an amine, and the resulting mixture is heated to a temperature of from 50° C. to 100° C., and preferably from 70° C. to 90° C., to reach a constant viscosity, and then is neutralized up to 100% with the amine. 
     
     
       10. The process according to claim 9 comprising: after said step of neutralizing said reacted mixture up to 100%, conducting a distillation to volatilize and remove said organic solvent or solvent mixture.   
     
     
       11. A coating composition consisting of a dispersion of cross-linked polymer microparticles, said polymer microparticles being prepared at an elevated temperature in an aqueous medium from two components, (A) and (B), the ratio by weight of component (A) to component (B) being between 30:70 and 95:5, said medium optionally containing still further film-forming material, pigments and further conventional additives, and being particularly suitable for producing protective and/or decorative coatings, wherein A. component (A) is a polymer, optionally dissolved in an organic solvent, said polymer bearing at least two hydroxyl groups and comprising a number of ionic groups sufficient for the formation of a stable aqueous dispersion, said polymer comprising a polyesterpolyol having an acid value between 20 and 50, said polyesterpolyol being prepared from one or more polyol(s) selected from the group consisting of: ethylene glycol, 1,2- and 1,3-propanediol, 1,3- and 1,4-butanediol, the isomeric pentanediols, hexanediols or octanediols (e.g., 2-ethyl-1,3hexanediol), trimethylolpropane, neopentyl glycol, glycerol, bishydroxymethyl cyclohexane, erythritol, mesoerythritol, arabitol, adonitol, xylitol, mannitol, sorbitol, dulcitol, hexanetriol, and (poly-)pentaerythritol, by reaction with polycarboxylic acid or anhydrides thereof--so far as said anhydrides exist--having from 2-18 carbon atoms, wherein said polycarboxylic acids and/or anhydrides thereof may be employed individually or in admixtures thereof; and component (B) is an aminoplast resin consisting of molecules containing at least two reactive groups consisting of hydroxyl and/or amino and/or ether groups,   the aqueous dispersion of cross-linked microparticles being stable.   
     
     
       12. The coating composition according to claim 11, characterized in that it contains metal pigment particles, and especially aluminum pigment particles. 
     
     
       13. A coating composition comprising a binder or thickener, said binder or thickener comprising the aqueous dispersion of claim 1 or claim 2.